Diesel-electric locomotives traditionally employ a high power diesel internal combustion engine to rotate an electric generator, which in turn provides electric power to drive the locomotive's fraction motors and to power other components. In a so-called line haul locomotives, the desired acceleration and pull force required to move rolling stock and cargo weighing hundreds of tons requires a large amount of power. For this reason, the diesel engine in a line haul locomotive often has a rated power output exceeding 4,000 brake horsepower (bhp).
Large diesel engines perform well in terms of emissions and fuel efficiency at or near the rated power output. But the duty cycle typically experienced by a line haul locomotive also requires the engine to idle for long periods of time or maintain low train speeds, which results in the diesel engine often operating at a low power output. During operation in low power output modes, the large diesel engine is relatively less effective in terms of emissions and fuel efficiency.
Several locomotive manufacturers in the U.S. have begun to commercialize new locomotives which are powered by multiple diesel engines. For instance, multi-engine “genset” locomotives have been developed for use in so-called switcher locomotive applications. Switcher locomotives are typically used in a rail yard to move cars around when assembling and disassembling trains. The relatively recently commercialized switcher locomotives are called genset locomotives because each engine is connected to device a respective electric generator. The multiple engines are typically mounted together on a separate frame as an independent power pack in a fashion similar to a generator set used in backup power or remote power applications. Each genset is individually mounted to the locomotive deck. Genset locomotives can have two to four separate power packs, which may be identical to one another or which may include a larger engine in combination with one or more smaller engines. Having multiple engines allows the operation of just a single engine during idling and low power output. The relatively small, single engine operated during low power output can operate more efficiently than a very large diesel engine at that same power output. A low power output will be a much higher percentage of the rated power of a small engine than it would be for a very large engine, and efficiency is generally a function of the percentage of rated power output. When the locomotive requires high power output, all of the engines can be operated simultaneously to produce maximum power. Thus, with the application of multiple engines, it is possible to reach a new compromise for locomotive propulsion where power can be provided almost as effectively, in terms of emissions and fuel efficiency, at low power output as at high power output.
The use of multiple engines and alternators in a single locomotive, however, creates a challenge for packaging of all the different components into the locomotive's engine compartment. Moreover, the dense packaging of engine and other locomotive components within the engine compartment creates challenges when attempting to access various components for repair and service.